The invention generally relates to data communication systems. More particularly, the invention involves a method and an apparatus for supporting intercom and conferencing between corded and cordless telephone handsets.
Private Branch Exchange (PBX) devices are used to expand the number of telephone handsets or sets which share a common Plain Old Telephone System (POTS) line or a set of POTS lines from a business or residence to a telephone company Central Office (CO) switch. PBX devices support features such as set-to-set intercom and set-to-CO conferencing.
Conventional analog techniques for generating local signals for intercom or summed signals for intercom require analog multiplexers and summing amplifiers. In contrast, digital techniques usually require high speed Digital Signal Processors (DSP). As such, there is difficulty in combining analog and digital techniques for generating intercom and conferencing signals.
Therefore, in a multi-handset hybrid telephone system supporting both analog and digital cordless telephone applications, the task of supporting intercom and conferencing features between corded and cordless telephones is problematic. A need exists in the art to support intercom and conferencing features between analog corded telephones and digital cordless telephones.
The invention overcomes the disadvantages of the prior art by providing a method and apparatus for combining corded and cordless telephone handsets in intercom and conferencing applications.
A first embodiment of the invention is a device that combines corded and cordless telephone handsets to analog network lines. Specifically, the device comprises a codec coupled to each analog network line, an analog to digital converter coupled to each corded telehone handset, a digital converter coupled to each cordless telephone handset, a signal processing circuit coupled to the codec, the analog to digital converter and the digital converter, and a controller coupled to the signal processing circuit, the codec, the analog to digital converter and the digital converter.
The codec digitizes a signal from the analog input line, the analog to digital converter digitizes a signal from the corded telephone handset and the digital converter demodulates and possibly decompresses a signal from the digital cordless telephone handset. These signals may comprise audio signals. The signal processing circuit receives the signals from the codec, analog to digital converter and digital converter during time division multiplexed (TDM) slots as determined by the controller. The number of time solts required is equal to the sum of corded telephone handsets, cordless telephone handsets and analog network lines.
The signal processing circuit then generates a set of output signals from the received signals. In operation, the signal processing circuit receives a signal during each time slot, multiplies the signal by a set of programmed coefficients to generate one output signal for each corded telephone handset, cordless telephone handset and analog network line. The circuit adds the products for each time frame to values from the previous time slot to provide a running total. As such, the signal processing circuit is generally a multiply and accumulate circuit.
The codec, analog to digital converter and digital converter then processes the output signals to the respective analog network lines, corded telephone handsets and cordless telephone handsets and cordless telephone handsets. These components operate in a reverse fashion to that previously described.
A second embodiment of the invention is a device that combines corded and cordless telephone handsets to a digital network. In this embodiment, the device comprises a digital interface coupled to the digital network, an analog to digital converter coupled to each corded telephone handset, a digital converter coupled to each cordless handset, signal processing circuit coupled to the digital interface as well as the analog to digital converter and the digital converter, and a digital signal processor coupled to the signal processing circuit as well as the digital interface.
The first and second embodiments are similar with the exception of this second embodiment comprising a digital interface instead of a codec, and a digital signal processor instead of a controller. The digital interface may comprise a cable modem or digital subscriber line (DSL) modem for decoding a signal from the digital network and a decompressor/compressor for decompressing a compressed audio signal from the network or compressing an audio signal to the network. The digital signal processor may packetize the signals from the digital interface, the analog converter and the digital converter in substantially the same manner as the controller in the first embodiment.